Re: xref and displaying locations in appropriate window or frame

[Juri Linkov]

> I hardly ever played around with IDEs so I wouldn't know.

Implementing an IDE-like mode in Emacs implies displaying the *xref*
buffer in the same fixed bottom window shared with all other view buffers
like *grep*, *compilation*, *Completions*, ...

 ------------
|  O  |   T  |
|     |      |
|------------|
|     X      |
 ------------

and using the tab-bar to switch between these buffers in that bottom window.

OTOH, in non-IDE mode let's use the default behavior of display-buffer to 
display
*xref* the same way as *grep* and *compilation* are displayed, i.e.:

 ------------
|     |      |
|  T  |   X  |
|     |      |
 ------------

or in narrow frames:

 -----
|  T  |
|-----|
|  X  |
 -----

One problem with xref is that currently it doesn't keep the *xref*
buffer displayed all the time during the next-error navigation,
and I don't understand why.